LCD

Komponendid

Monitoril on vähemalt 2 mikroskeemi. Üks neist on loogika skeem, mille külge ühendatakse VGA või DVI kaabel. Teine on toiteplokk/taustavalguse voolu muundur. Mõnel juhul on taustvaluse osa toiteplokist eraldi.

The Power supply board: Muundab vahelduvvoolu AC (120V või 240V) kõrgpingeks DC

by the bridge rectifiers to be used by the switching power supply circuits that converts this DC voltage into high frequency (around 50~100 KHz) AC for driving the step down transformer.

Tavaliselt tekitatakse kaks väljundpinget: 5vdc loogika skeemile ja 12~20vdc (12vdc kuni 17", 16~24vdc 18~24" ekraanile).

Toiteplokk on monitoril alati voolu all (kui pole kasutusel sellist lülitit, mis reaalselt võtab monitoril voolu ära), mistõttu on see töös 24/7 sõltumata monitori kasutusest, ning kõiksugused voolu kõikumised jõuavad toiteplokini.

Taustavalguse inverteri skeem: Kaksutades 12~24vdc muundatakse see kõrgsageduslikuks vahelduvvooluks AC et juhtida inverteri trahvosid CCFL (Cold Cathode Fluorescent Lamp) assemblies#.

Trahvod juhivad CCFL lampe, andes alustuseks 1500~2000v pinget, ning hiljem 500~800v.

3) Logic board: The logic board get the signals from the VGA (ANALOG) or DVI (DIGITAL) and processes them and feed them to the LCD panel T-CON (Timing Controller) board on the back of the LCD panel. It also sends out two signals (backlight ON/OFF and Dimming) to the inverter circuits when the monitor is on and getting the signals from the PC. If the logic board does not get the signal from the PC, it will put monitor into standby mode. The 5vdc feeding it is converted to 3.3v, 1.8vdc by the switching buck converters to run the processor. The logic board also sends the 5vd or 12vdc power for the T-CON board, if the voltage is not there, you will see white/grey glowing screen only. Not much repair you can do on the logic board unless you have the full service manual and surface mount repair station.

4) CCFL and Inverter circuits testing: If you don not have the inverter and lamp tester boxes (see www.lcdparts.net), you may be able to do a simple test by using these steps: If the screen flashes on for a second, you can disconnect all the lamp connectors and connect it into one of the transformer output connector and see if you will see the flash on the screen, if you do, then try it with another transformer output connector to see if it also get the flash on the screen. Repeat the procedure with other 3 lamps. If all the lamps do flash on for seconds then more likely the lamps are OK. If lamp only flash on one of the transformer output then you will know that the problem in that transformer inverter circuits. If none of the lamps flash at all then the problem is in the inverter circuits, power supply, or not getting the on signal from the logic board.

Probleemid

Common problems: Blown fuses, bad caps (leaking/bulging tops or bottom seals, please note that bad cap may look normal but it can have high ESR (Equivalent Series Resistance). The DC filter cap should be low ESR type for using in the switching power supply; general purpose electrolytic types will not last very long in switching power supply circuits. Poor solder joints, over heated components.

Testing: Plug the monitor in but do not activate the power switch so the backlight inverter circuits will be off. Check the 5vdc and the 12~24vdc to make sure they are OK. They should be tested with the load, you can use 6V 1A (6watts) lamp for the 5vdc, and car lamps such as 1157 (12v 8watts lo/26watts high) turn signal brake lamp using high filament connection for testing the 12~18vdc (or use two 1157 in series for 19~24vdc) for the backlight inverter circuits. If the power supplies are working, the output voltages should be steady at the rated voltages. The power supply will go into shut down if it detects too much current draw due to false in the power supply or short circuits in the backlight inverter or in the logic board.

Lingid

http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting